GB2134991A - Circulating pump - Google Patents

Abstract

A pump which is driven by an electric motor whose rotor (16) is journalled at both ends of its shaft (17) by pairs of oppositely polarised, annular permanent magnets (9, 18 and 15, 18). <IMAGE>

Description

SPECIFICATION Circulating pump The invention relates to circulating pumps of the typefor use, for example, in domestic water and small heating circuits.

Circulating pumps ofthistype usually have a fixed stator assembly, a winding which is distributed around the circumference of the bore in the stator assembly and which produces a rotating magnetic field, and a rotatable rotorwhich is driven by the magnetic field.

Starting problems frequently occur in small circulating pumps, particularly those having electric drive motorswhosepowerinputPis lessthan 30 watts, since the journal of the rotor, which is frequently received in a ceramic bearing, first has to float. A problemwhich arises in such motorsisthatsmall particles of dirt can be deposited in the bearings, or can even entertheairgap between the rotorandthe stator, particularly after a long inoperative period.

An object of the present invention is to construct the electric drive motor of a circulating pump such that reliable starting is ensured despite the small dimensions ofthe drive motor and the small values ofthe air gap occasioned thereby, even in the event of small foreign bodies having become deposited in the bearing air gap or machine air gap.

In accordance with the present invention, there is provided a circulating pump for domestic water comprising a fixed annular stator assembly having a winding which is distributed around the circumference of the bore in the stator assembly and which produces a rotating magnetic field, and a rotor which has a cylindrical circumferential surface and which is driven by the rotating magnetic field and islournalled at the two ends of its shaft by respective bearings, each of the bearings comprising a first permanent magnet connected to the rotor and surrounded buy a fixed, second annular permanent magnet, with an at least approximately constant radial air gap therebetween, the two permanent magnets associated with each bearing being radially polarised, with their like pole surfaces located opposite to one another.

A particularly small magnetic air gap, which does not require anyfinishing by grinding orthe like, is achieved when the air gap between the permanent magnets, associated with a respective bearing, forms a frustum whose base faces the associated end of the rotor.

The invention will be described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. lisa diagrammatic longitudinal section of one embodiment of a pump motor in accordance with the invention; and Fig. 2 is a diagrammaticview of a further embodiment ofthe invention in longitudinal section.

The illustratedcirculating pump is intended for operating with domestic water and has a pump housing7 having an axial inletZand a radial outlet A forthe domestic water which is indicated by arrows and which is delivered by an impeller. The pump P is driven by an electric motorwhich operates on the induction principle and whose rotor has magnetic bearings as described further hereinafter.

Figure lisa section through the circulating pump. A stator 1 having windings 2 is pressed against a base part4 of the housing 7 by an annular shoulder 6 on a cover3. Pressed-in sheet metal tongues 5 hold togetherthe base part 4 ofthe housing and the cover 3. An outer bearing ring 9 in the form of a first, annular permanent magnet is pressed against a shoulder 10 in an anti-magnetic splittube 11 by means of an annular retaining plate 8 located bythe pump housing 7. The pump housing 7 also presses an O-ring seal 12 against a flange 13 at one end ofthe split tube 11.The other end ofthe splittube 11 is sealed in a water-tight manner relative to a second outer bearing ring 15 by meansofawelded-on orsoldered bearing pot 14.The outer bearing ring 15 is again in the form of an annular permanent magnet. Inner bearing rings 18, which are again in the form of annular permanent magnets, are secured to ends 17 ofthe shaft of the rotor 16. The two permanent magnets associated with each bearing are radially polarised, with their like pole surfaces located opposite to one another. An at least approximately constant radial air gap is developed between the facing surfaces ofthe permanent magnets. In orderto increase the residual induction ofthe permanent magnets, the latter are composed of individual segments having a preferred magnetic direction.

Figure 2 shows a modified construction in which the outer rings 9,15 ofthe bearings are embedded in resilient plastics material parts 19, 20 inserted into the slotted tube 11. Respective sealing rings 21 and 22 can be provided by suitable design of those surfaces ofthe plastics parts 19,20 which face the slotted tube, as is shown in Figure 2.

The rotor can bejournalled in a contactless manner by virtue ofthe proposed solution, whereby no special demands with respectto starting torque are made on the electric machine. The electric machine may be designed exclusively in accordance with the criteria of continuous operation. This results in energy-saving machines which are smallerthan conventional machines. As a result ofthe resilience of the magnetic bearings, the rotor can perform tumbling movements if a foreign body should enter the air gap ofthe machine, and can free itself again.

Both axial and radial guiding ofthe rotor can be achieved when the surfaces of the bearings defining the air gaps are ofcircularfrusto-conical configuration. The load-bearing capacity and the rigidity in an axial and a radial direction can be determined by suitable choice ofthe angle between the surface ofthe cone and the axis of rotation and by the size of the surface of the magnet. By virtue ofthe contactless journalling ofthe rotor,thesetypes of pumps are distinguished by a low level of noise. If required, the cavity between the splittube and the housing can be filled with a satisfactorily thermally conductive synthetic resin in orderto preventanyformation of condensation which might impair the insulation strength ofthewinding.

In the proposed solution, there is no need to provide a conventional screw cover which is provided in most pumps at the side ofthe housing remote from the pump and through which a jammed rotorcan be rendered operative again by means of a screwdriver orthelike.

Claims (5)

1. A circulating pumpfordomesticwater compris- ing a fixed afixed annularstatorassemblyhaving a winding which is distributed around the circumference of the bore in the stator assembly and which produces a rotating magneticfield, and a rotor which has a cylindrical circumferential surface and which is driven bythe rotating magneticfield and isjournalled at the two ends of its shaft by respective bearings, each of the bearings comprising a first permanent magnet connected to the rotor and surrounded by a fixed, second annular permanent magnet, with an at least approximately constant radial air gap therebetween, the two permanent magnets associated with each bearing being radially polarised, with their like pole surfaces located opposite to one another.

2. A pump as claimed in claim 1, wherein the annular halves of the bearings of permanent magnet material are composed of isotropic, circular, frusto- conical permanent magnet segments for the purpose of the increasing the residual induction.

3. A pump as claimed in claim 2, wherein the air gap ofthe bearing is formed bythe surfaces oftwo frustums which are coaxial with the axis of rotation of the rotor and whose bases are adjacent to the end faces ofthestatorassembly.

4. A pump as claimed in claim 3, wherein the surface ofthe cone forms an angle of approximately 1 0 to 30 with the axis ofthe rotor.

5. A circulating pump substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or in Fig. 2 of the accompanying drawings.